Massive multiple-input multiple-output (MIMO) has been identified as one of the indispensable technologies to support ultra-high data rate for a huge number of mobile users in the 5G wireless networks. In this talk I will focus on our novel pilot sequence design to mitigate pilot contamination in multi-cell multiuser massive MIMO networks. Our proposed design generates pilot sequences for all users in the multi-cell network and devises power allocation at base stations for downlink transmission. The pilot sequences together with the power allocation ensure that the user capacity of the network is achieved and the predefined signal-to-interference-plus-noise ratio requirements of all users are met. To realise our design, we derive new closed-form expressions for the user capacity and the capacity region of the network, built upon which we develop a new algorithm to obtain the required pilot sequences and power allocation. Numerical results are presented to corroborate our analysis and to explicitly examine the impact of key parameters, such as the pilot sequence length and the total number of users, on the network performance.