System and method for controlling network traffic by restricting a set of cyclic shifts for long-term evolution (LTE) physical random access channel (PRACH) preambles

1. A method for calculating random access preambles based on cyclic shifts, wherein the calculation of cyclic shifts for restricted sets is based on C v =d start └v/n shift RA ┘+(v mod n shift RA )N CS v=0.1, . . . , n shift RA n group RA + n shift RA −1, wherein a first and a second restricted set of cyclic shifts can be generated, wherein, an indicator in configuration parameters indicates whether the second restricted set of cyclic shifts should be generated, wherein the calculation of at least two of the parameters n shift RA , d shift ,n group RA , n shift RA is different for the first and the second set of cyclic shifts, the method comprising:

determining, by one or more processors of at least one network node, if the indicator indicates whether the second restricted set of cyclic shifts should be generated, and

if so, calculating, by the one or more processors, cyclic shifts of the second restricted set based on: for N CS ≤d u <N ZC /S parameters are determined according to:

n shift RA =└ d u /N CS ┘

d start =4 d u +n shift RA N CS

n shift RA =└N ZC /d start ┘

n shift RA =max(└( N ZC −4 d v −n group RA d start )/ N CS ┘0),

wherein N ZC represents a random access preamble sequence length, N CS represents a configured cyclic shift, value for a restricted set, and cyclic shift d u represents a cyclic shift dependent on N ZC ,

controlling, by the one or more processors, network traffic using the random access preambles, and

wherein a different calculation for a parameter is performed by using a different equation for calculating the parameter for the second restricted set of cyclic shifts as compared to the calculation of the same parameter for the first restricted set of cyclic shifts,

the restricted sets being suitable for high speed travel to support uplink frequency offset for a physical random access channel (PRACH) subcarrier spacing, the uplink frequency offset between the cyclic shifts of the restricted set of the preamble sequences being configured to be larger than the Doppler shift associated the high speed travel.

2. The method of claim 1 , further comprising:

calculating cyclic shifts of the second restricted set based on: for N ZC /5≤d u ≤(N ZC −N CS )/4 parameters are determined according to:

n shift RA ×└( N ZC −4 d u )/ N CS ┘

d start =N ZC −4 d u +n shift RA N CS

n group RA =└d u /d start ┘

n shift RA =min(max(└( d u −n group RA d start ) /N CS ┘, 0), n shift RA ).

3. The method of claim 1 , further comprising:

determining the random access preamble sequence length N ZC based on a configured preamble format.

4. The method of claim 1 , further comprising:

determining the cyclic shift N CS for the restricted set based on a configured Zero Correlation Zone Configuration index.

5. The method of claim 1 , further comprising:

determining cyclic shift d u as follows:

d

u

=

{

r

0

≤

r

<

N

ZC

/

2

N

ZC

-

r

otherwise

where r may be the smallest non-negative integer that fulfils (ru)mod N ZC =1.

6. The method of claim 1 , further comprising:

calculating random access preambles based on a root Zadoff-Chu sequence by the following cyclic shifts:

x u,v ( n )= x u (( n+C v )mod N ZC ).

7. User Equipment (UE), comprising:

one or more processors configured to,

receive, from a network node, an indicator for calculating a second set of preamble sequences by a method according to claim 1 and which the UE is allowed to use,

calculate and select a preamble out of the indicated allowed preamble sequences, and

send a physical layer random access preamble representing the selected preamble through a physical random access channel (PRACH) to the network node.

8. The UE of claim 7 , wherein the one or more processors are further configured to,

receive, from the network node, a PRACH configuration including the indicator.

9. The method of claim 1 , wherein the uplink frequency offset is in a range of −2.5 KHz to +2.5 KHz.

10. The method of claim 1 , wherein the uplink frequency offset is at least twice a PRACH subcarrier spacing.

11. An apparatus, comprising:

one or more processors configured to,

calculate random access preambles based on cyclic shifts, wherein the calculation of cyclic shifts for restricted sets is based on C v =d start └v/n shift RA ┘+(v mod n shift RA )N CS v=0,1, . . . , n shift RA n group RA + n shift RA −1, wherein a first and a second restricted set of cyclic shifts can be generated, wherein an indicator in configuration parameters indicates whether the second restricted set of cyclic shifts should be generated, wherein the calculation of at least two of the parameters n shift RA , d start , n group RA , n shift RA is different for the first and the second set of cyclic shifts, wherein the one or more processors are further configured to,

determine if the indicator indicates whether the second restricted set of cyclic shifts should be generated, and

if so, calculate cyclic shifts of the second restricted set based on: for N CS ≤d u <N ZC /5 parameters are determined according to:

n shift RA =└d u /N CS ┘

d start =4 d u +n shift RA N CS

n group RA =└N ZC /d start ┘

n shift RA =max(└( N ZC −4 d u −n group RA d start ) /N CS ┘0),

wherein

N ZC represents a random access preamble sequence length, N CS represents a configured cyclic shift value for a restricted set, and cyclic shift d u represents a cyclic shift dependent on N ZC , and

control network traffic using the random access preambles, and wherein a different calculation for a parameter is performed by using a different equation for calculating the parameter for the second restricted set of cyclic shifts as compared to the calculation of the same parameter for the first restricted set of cyclic shifts,

the restricted sets being suitable for high speed travel to support uplink frequency offset for a physical random access channel (PRACH) subcarrier spacing, the unlink frequency offset between the cyclic shifts of the restricted set of the preamble sequences being configure to be larger than the Doppler shift associated with the high speed travel.

12. The apparatus of claim 11 , wherein the uplink frequency offset is in a range of −2.5 KHz to +2.5 KHz.

13. The apparatus of claim 11 , wherein the uplink frequency offset is at least twice a PRACH subcarrier spacing.