1. A method for a network node for generating a scheduling grant for a wireless device of a communication system, wherein the communication system supports variable Transmission Time Interval (TTI) lengths to be transmitted in one TTI, the method comprising:determining a TTI length for a scheduled TTI, wherein the TTI length is determined in number of symbols;
determining at least one reference signal parameter for the scheduled TTI, wherein the at least one reference symbol parameter is selected from a reference symbol position and a reference symbol cyclic shift;
accessing at least one mapping associating TTI indices, TTI lengths and one or more reference symbol parameters; and
encoding the TTI length and the at least one reference symbol parameter into a TTI index,
wherein the TTI length and the one or more reference symbol parameters are encoded into the TTI index using the at least one mapping.