Method and apparatus for accessing a wireless communication system
View Patent ↗Access to a wireless communication system ( 100 ) by a subscriber station ( 101 - 103 ) is facilitated by selecting ( 705 ) an access sequence from a set of sequences that have been identified to have a low average of peak-to-average-power-ratios of access signals generated by the set of sequences and also based on a good cross-correlation of the access signals; forming ( 714 ) the access waveform by generating an access signal using the access sequence and appending in the time domain a cyclic prefix to the access signal; and transmitting ( 715 ) the access waveform. In some implementations, the access waveform is cyclically shifted ( 820 ) before the cyclic prefix is appended, and in some implementations, the signal is transmitted ( 710, 810 ) in a randomly selected sub-band of an access interval.
1. A method used by a subscriber station in a wireless communication system for accessing the communication system, comprising:
selecting an access sequence from a set of N c access sequences that have been identified to have a low average of peak-to-average-power-ratios of access signals generated by the set of N c access sequences and to have good cross-correlation of the access signals generated by the set of N c access sequences, and wherein the set of N c access sequences has been generated by a corresponding set of sequences of length K, wherein K is a quantity of sub-carriers identified for transmitting an access signal;
forming the access waveform by generating an access signal using the access sequence and appending in the time domain a cyclic prefix to the access signal; and
transmitting the access waveform, wherein the corresponding set of sequences of length K is based on a set of (N G −1) Generalized Chirp Like (GCL) sequences that are defined as:
s
u
(
k
)
=
exp
{
-
j2π
u
k
(
k
+
1
)
2
N
G
}
,
k
=
0
…
N
G
-
1
and
u
(
“
class
index
”
)
=
1
…
N
G
-
1
wherein N G is a prime number that is one of the next number larger than K that is prime, the next number smaller than K that is prime, and K when K is prime.
2. The method according to claim 1 , wherein the access signal is generated by performing an Inverse Fast Fourier Transform on a frequency domain sequence formed from the access sequence.
3. The method according to claim 1 , further comprising selecting at random a frequency sub-band having K sub-carriers from among N b1 sub-bands.
4. The method according to claim 1 , wherein the selection of the access sequence from the set of N c access sequences is made as a random selection among the N c access sequences.
5. The method according to claim 1 , wherein the low average of the peak-to-average-power-ratios of the entire set of N c access signal is less than 6 dB.
6. The method according to claim 1 , wherein when N G is larger than K, the corresponding set of sequences of length K is generated by truncating the set of GCL sequences to length K.
7. The method according to claim 1 , wherein when N G is smaller than K, the corresponding set of sequences of length K is generated by copying (K−N G ) terms from the beginning of each GCL sequence and appending them to the end.
8. The method according to claim 1 , wherein the corresponding set of sequences of length K is generated by a random phase shift keyed sequence or a Golay phase shift keyed sequence.
9. The method according to claim 1 , further comprising cyclically time shifting the access signal by a shift value that is one of a defined set of N sh shift values.
10. The method according to claim 1 wherein the length of the cyclic prefix appended to the access signal in the time domain is determined based on the maximum timing difference among all possible subscriber locations and the excessive delay spread of the channel in the deployment environment.
11. The method according to claim 1 wherein the accessing of the communication system is by one of a random transmission and an assigned uplink transmission.
12. A method used by a subscriber station in a wireless communication system for accessing the communication system, comprising:
selecting an access sequence from a set of N c access sequences;
generating an access signal by performing an Inverse Fast Fourier Transform of the selected access sequence;
cyclically time shifting the generated access signal by a shift value that is one of a defined set of N sh shift values;
forming an access waveform by appending a cyclic prefix to the selected cyclically shifted access signal; and
transmitting the access waveform, wherein the number of shift values N sh is determined based on └N sp /L CPe ┘, wherein N sp is the Fast Fourier Transform size of a special Fast Fourier Transformation window, and L CPe is a length of an extended cyclic prefix of a special orthogonal frequency division multiplex symbol.
13. A method used by a subscriber station in a wireless communication system for accessing the communication system, comprising:
selecting an access sequence from a set of N c access sequences;
generating an access signal by performing an Inverse Fast Fourier Transform of the selected access sequence;
cyclically time shifting the generated access signal by a shift value that is one of a defined set of N sh shift values;
forming an access waveform by appending a cyclic prefix to the selected cyclically shifted access signal; and
transmitting the access waveform, wherein the number of shift values N sh is determined based on └N sp /L CP ┘, wherein N sp is the Fast Fourier Transform size of a special Fast Fourier Transformation window, and L CP is determined based on an excessive delay spread of the channels encountered in a deployment.
14. The method according to claim 12 , further comprising selecting at random a frequency sub-band having K sub-carriers from among N b1 sub-bands.
15. The method according to claim 13 , further comprising selecting at random a frequency sub-band having K sub-carriers from among N b1 sub-bands.
16. A method used by a base station in a wireless communication system for facilitating an access of the communication system by a subscriber station comprising:
receiving an access signal from the subscriber station in an access waveform, wherein the access waveform has been formed by
selecting an access sequence from a set of N c access sequences that have been identified to have a low average of peak-to-average-power-ratios of access signals generated by the set of N c access sequences and to have good cross-correlation of the access signals generated by the set of N c access sequences, and wherein the set of N c access sequences has been generated by a corresponding set of sequences of length K, wherein K is a quantity of sub-carriers identified for transmitting an access signal;
forming the access waveform by generating an access signal using the access sequence and appending in the time domain a cyclic prefix to the access signal; and
transmitting the access waveform, wherein the corresponding set of sequences of length K is based on a set of (N G −1) Generalized Chirp Like (GCL) sequences that are defined as:
s
u
(
k
)
=
exp
{
-
j
2
π
u
k
(
k
+
1
)
2
N
G
}
,
k
=
0
…
N
G
-
1
and
(
“
class
index
”
)
=
1
…
N
G
-
1
wherein N G is a prime number that is one of the next number larger than K that is prime, the next number smaller than K that is prime, and K when K is prime; and
analyzing the access signal to identify the selected access sequence.
17. The method according to claim 16 , further comprising processing the access signal to extract subscriber station synchronization information.
18. The method according to claim 17 , wherein the subscriber station synchronization information is at least one of timing, power, frequency offset, and channel impulse response.
19. The method according to claim 1 , wherein the set of access sequences of length K based on a set of (N G −1) GCL sequences are obtained from a transformation of the set of GCL sequences.
20. The method according to claim 19 , wherein the transformation comprises one of a Discrete Fourier Transformation and applying a unitary matrix on a GCL sequence.
21. A subscriber station, comprising:
a processor that:
selects an access sequence from a set of N c access sequences that have been identified to have a low average of peak-to-average-power-ratios of access signals generated by the set of N c access sequences and to have good cross-correlation of the access signals generated by the set of N c access sequences, and wherein the set of N c access sequences has been generated by a corresponding set of sequences of length K, wherein K is a quantity of sub-carriers identified for transmitting an access signal, and
forms the access waveform by generating an access signal using the access sequence and appending in the time domain a cyclic prefix to the access signal; and
a transmitter that transmits the access waveform,
wherein the corresponding set of sequences of length K is based on a set of (N G −1) Generalized Chirp Like (GCL) sequences that are defined as:
s
u
(
k
)
=
exp
{
-
j2
π
u
k
(
k
+
1
)
2
N
G
}
,
k
=
0
…
N
G
-
1
and
u
(
“
class
index
”
)
=
1
…
N
G
-
1
wherein N G is a prime number that is one of the next number larger than K that is prime and the next number smaller than K that is prime, and K when K is prime.