Enhanced PRACH preamble format
The present invention relates to a user terminal, UE, in a wireless communication system ( 1 ). The user terminal ( 4 a, 4 b ) comprises a receiver unit ( 5 a, 5 b ), a transmitter unit ( 6 a, 6 b ) configured to transmit data in transmit sub-frames occurring at defined sub-frame intervals, and a control unit ( 7 a, 7 b ) configured to control the receiver circuit ( 5 a, 5 b ) and the transmitter circuit ( 6 a, 6 b ). The control unit ( 7 a, 7 b ) is also configured to create a PRACH, Physical Random-Access Channel, preamble ( 27 ) as an uplink transmission to a node ( 2 ) that is arranged to receive communication from the user terminal in said sub-frames. This communication comprises OFDM, Orthogonal Frequency-Division Multiplexing, based symbols ( 20 ). The control unit ( 7 a, 7 b ) is configured to create each PRACH preamble ( 27 ) such that is comprises a sequence of a plurality of identical random access sequences (s(n)), where each random access sequence (s(n)) has the same length in time as each one of the OFDM based symbols ( 20 a, 20 b, 20 c ). The present invention also relates to a corresponding method.
1. A user terminal (UE) in a wireless communication system, the user terminal comprising:
a receiver circuit;
a transmitter circuit configured to transmit data in transmit sub-frames that occur at defined sub-frame intervals and that comprise a plurality of Orthogonal Frequency-Division Multiplexing (OFDM) symbols;
a control circuit configured to control the receiver circuit and the transmitter circuit;
wherein the control circuit is also configured to create a Physical Random-Access CHannel (PRACH) preamble as an uplink transmission to a node that is arranged to receive communication from the user terminal in the OFDM symbols of the sub-frames; and
wherein the control circuit is further configured to create each PRACH preamble from a sequence comprising a plurality of identical random access sequences, where each random access sequence has the same length in time as one of the OFDM symbols.
2. The user terminal of claim 1 , wherein the user terminal is configured to transmit one PRACH preamble in one sub-frame.
3. The user terminal of claim 1 , wherein the user terminal is configured to transmit one of two PRACH preambles, chosen from a set of possible PRACH preambles, in one sub-frame; the two possible PRACH preambles having mutually different random access sequences.
4. The user terminal of claim 3 , wherein the user terminal is configured to transmit the chosen PRACH preamble at one of two or more possible different frequency bands.
5. The user terminal of claim 3 , wherein the chosen PRACH preamble is shortened such that it begins later in the corresponding sub-frame by means of an initial guard time.
6. The user terminal of claim 3 , wherein each PRACH preamble further comprises a cyclic prefix that precedes the sequence comprising the plurality of identical random access sequences.
7. The user terminal of claim 3 , wherein each PRACH preamble comprises a plurality of random access sequences succeeded by a final part that is part of one of the random access sequences, the final part being inserted at the end of the PRACH preamble such that the PRACH preamble covers a whole length of a last Fast Fourier Transform window.
8. The user terminal of claim 1 :
wherein each random access sequence is defined by means of a Zadoff-Chu sequence, where the u th root Zadoff-Chu sequence is defined as
x
u
(
n
)
=
ⅇ
-
j
π
un
(
n
+
1
)
N
ZC
,
0
≤
n
≤
N
ZC
-
1
,
where a length N ZC of the Zadoff-Chu sequence is a prime number;
wherein a time-continuous random access sequence s(t) is defined by
s
short
(
t
)
=
β
PRACH
∑
k
=
0
N
ZC
-
1
∑
n
=
0
N
ZC
-
1
x
u
(
n
)
·
ⅇ
-
j
2
π
nk
N
ZC
·
ⅇ
j2π
(
k
+
k
0
)
Δ
ft
;
where 0≤t<T short , β PRACH is an amplitude-scaling factor in order to conform to the transmit power of PRACH, k 0 =n PRB RA N sc RB −N RB UL N sc RB /2, and Δf is the sub-carrier spacing, where the location in the frequency domain is controlled by a parameter n PRB RA ; a resource block size in the frequency domain, expressed as a number of subcarriers, is denoted by n sc b , and an uplink bandwidth configuration, expressed in multiples of N sc RB is denoted by N RB UL .
9. A method for transmitting a Physical Random-Access Channel (PRACH) preamble from a user terminal (UE) to a node in a wireless communication system, the method comprising:
creating a PRACH preamble from a sequence comprising a plurality of identical random access sequences, where each random access sequence has the same length in time as one Orthogonal Frequency-Division Multiplexing (OFDM) symbol used by the UE to transmit data during sub-frames that occur at defined sub-frame intervals and that comprise a plurality of the OFDM symbols; and
transmitting the PRACH preamble during one sub-frame.
10. The method of claim 9 , further comprising transmitting one of two PRACH preambles, chosen from a set of possible PRACH preambles, in one sub-frame, the two possible PRACH preambles having mutually different random access sequences.
11. The method of claim 10 , further comprising transmitting the chosen PRACH preamble at one of two or more possible different frequency bands.
12. The method of claim 10 , further comprising shortening the chosen PRACH preamble such that it begins later in the corresponding sub-frame by means of an initial guard time.
13. The method of claim 10 , wherein each PRACH preamble further comprises a cyclic prefix that precedes the sequence comprising the plurality of identical random access sequences.
14. The method of claim 9 , wherein each PRACH preamble has a plurality of random access sequences succeeded by a final part that is part of one of the random access sequences, the final part being inserted at the end of the PRACH preamble such that the PRACH preamble covers a whole length of a last Fast Fourier Transform window.
15. The method of claim 9 , further comprising:
creating each random access sequence from a Zadoff-Chu sequence, where the u th root Zadoff-Chu sequence is defined as
x
u
(
n
)
=
ⅇ
-
j
π
un
(
n
+
1
)
N
ZC
,
0
≤
n
≤
N
ZC
-
1
,
where a length N ZC of the Zadoff-Chu sequence is a prime number;
wherein a time-continuous random access sequence s(t) is defined by
s
short
(
t
)
=
β
PRACH
∑
k
=
0
N
ZC
-
1
∑
n
=
0
N
ZC
-
1
x
u
(
n
)
·
ⅇ
-
j
2
π
nk
N
ZC
·
ⅇ
j2π
(
k
+
k
0
)
Δ
ft
,
where 0≤t<T short , β PRACH is an amplitude-scaling factor in order to conform to the transmit power of PRACH, k 0 =n PRB RA N sc RB −N RB UL N sc RB /2, and Δf is the sub-carrier spacing, where the location in the frequency domain is controlled by a parameter n PRB RA ; a resource block size in the frequency domain, expressed as a number of subcarriers, is denoted by N sc RB , and an uplink bandwidth configuration, expressed in multiples of N sc RB is denoted by N RB UL .