A321
Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter
Flight Crew Took Evasive Action
Environment - Non Weather Related
We were given the GRNPA ONE RNAV ARRIVAL into LAS by Los Angeles Center and told to cross LUXOR at 250 KTS at 12;000 FT. Furthermore; we were given a speed reduction to Mach .76 for spacing into LAS. We programmed in the crossing restriction and speed properly and started a managed descent to comply with the crossing restriction. Soon after we started the descent the aircraft rolled abruptly in a moderate manner for about 10-15 seconds. Both the Captain and I noted that it was the wake turbulence from the aircraft in front of us. The Captain told me that if it were to continue to do a V/S descent at 1;000 FT to get above the other aircraft's descent path so we are not following the same path of the aircraft in front of us the whole way down into LAS and exposing ourselves to wake turbulence dangers in doing so. Sure enough; a minute or two later; we get another roll (this time more severe than the last one) from the wake turbulence from the aircraft in front of us.To safely stay out of the wake turbulence; I put the aircraft in a V/S descent mode for 1;000 FT a minute to get above the aircraft in front of us. At that time the Captain advised Center what we were doing and why we were doing it and told Center that it may be difficult for us to cross LUXOR at 12;000 FT. Center told the Captain to contact Approach Control and advise them of the situation. Once the Captain switched over to approach the frequency was extremely busy and he could not get a word in. Meanwhile; I went back to managed descent as we were above the aircraft's path ahead of us. All in all; we may have missed the crossing restriction by a few hundred feet. Once again; the reason we missed the restriction was the need to stay out of the wake turbulence from the aircraft in front of us.
An A321 First Officer reported encountering wake vortex from preceding aircraft on arrival to LAS that was a factor in missing a crossing restriction.