A communication system includes a trainee communications device and one or more trainer communications devices. The trainee communications device announces a first period of time for beamforming training, switches a receiving antenna pattern to a sector and stays in the sector for a second period of time. The trainer communications devices transmit one or more predetermined bit sequences in the first period of time. The predetermined bit sequences are transmitted in at least one sector. Each of the predetermined bit sequences carries an identifier identifying the transmitting trainer communications device. The trainee communications device further estimates channel characteristics and computes receiving antenna weighting vectors of the trainer communications devices by using the received predetermined bit sequences, respectively, and the trainer communications devices obtain pertinent information including the estimated channel characteristics and receiving time of the predetermined bit sequences about beamforming training from the trainee communications device.