DICE has release the Squad Join features for Battlefield 4 on all platforms. This feature allows players to create and join squads before entering a game. In the video detailing the features (below), DICE says that the Squad Join feature was designed to keep friends from getting separated in Battlefield 4.
For players who miss getting into the squad before a game, they can join after the fact if space is available, and will be placed in the game, in the squad with their friends.
Squad Join is a feature that many Battlefield 4 players have been asking for since launch, and one of the many fixes that DICE has made recently to the game. They most recently implemented new servers on the shooter to remedy rubberbanding and lag.