Power and resource efficient uplink DMRS sequences for IFDMA

A method in a wireless device for transmitting demodulation reference signals (DMRS) over one, three or five resource blocks (RBs) with interleaved Frequency Division Multiple Access (IFDMA) in a wireless network wherein Single Carrier Frequency Division Multiple Access (SC-OFDMA) is deployed in an uplink, the method comprising:

• receiving, from the network node, an indication of using IFDMA for DMRS transmission;
• determining a set of base sequences, the set of base sequences comprising thirty quadrature phase shift keying, QPSK, sequences of length 6, 18 or 30;
• deriving a demodulation reference signal sequence from the set of base sequences;
• time multiplexing the demodulation reference signal sequence in single carrier-orthogonal frequency division multiplexing, SC-OFDM, symbols;
• transmitting, by a wireless device, the multiplexed signal to the wireless network node;
• the set of base sequences being given by:
• ru,v(n)=ejφ(n)π/4,0≤n≤MscRS−1,MscRS∈{6,18,30};v=0,u=0,1, . . . ,29,
• Where ru,v(n) is an equation for reference signal sequences;
• where MscRS is a sequence length;
• where v is a base sequence number;
• where u is a group number;
• and
• where φ(n) is given in a predetermined table.