Adaptive Compensation for Downlink Broadcast Signaling in the Narrow-beam Communication

Narrow-beam communication has been widely applied in many fields which provides a long transmission distance. However, the downlink broadcast signaling before communication limits the coverage expansion since the transmission distance of broadcast is much shorter. In this paper, we analyze the performance differences of narrow-beam unicast and circular-beam broadcast and investigate the reason for these differences. We divide the data channel with narrow-beam unicast and the control channel with circular-beam broadcast. Then we propose an adaptive compensation method to eliminate the differences on the transmission distance. We adopt the two-step adjustment based on the received power spectral density which is fed back from user terminals. The spread spectrum coding is first used on the control channel to increase its transmission antenna gains. Then we reallocate the power for channels to make sure that user terminals can obtain the same received power spectral density on two kind of channels. In this case, we can achieve the same transmission distance for narrow-beam unicast and circular-beam broadcast which means the system downlink transmission distance reach the optimum. The numerical results show that the proposed optimization method is feasible and can eliminate the performance differences.