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Abstract
In millimeter wave (mmWave) communications, the beamforming gains of large-scale antenna arrays are used to combat severe path losses and improve communication link quality. This requires beam training (BT) to determine the optimal beam direction and achieve beam alignment. The hierarchical codebook with multi-resolution training beams is widely used in BT to reduce training overhead. Unfortunately, due to hardware restrictions, the transition area between two adjacent training beams often leads to error propagation in a traditional BT scheme, which limits the accuracy of beam alignment. In this paper, we propose an improved BT scheme under hierarchical codebook. First, we define an index to measure the power difference of the received signals. Once the index is lower than the predefined threshold, the optimal beam direction is considered to be in the transition area, and an extra interval that contains the transition area is proposed for further beam searching. Then, we analyze the optimal threshold and the probability of beam misalignment based on the ideal beam pattern, proving that the error rate exponentially decreases with the signal-to-noise ratio (SNR) under a single-path channel with constant gain. Finally, simulation results demonstrate that the proposed scheme can significantly improve the accuracy of beam alignment and is applicable to most existing beam patterns.
Highlights
Millimeter wave communication is regarded as one of the most promising technologies for future wireless communication systems, and its abundant spectrum resources can significantly increase system capacity [1], [2]
To verify that beam training with overlapping interval (BTOI) is applicable to beam patterns under different hardware architectures, the DEACT codebook in [11], the beam widening via single-RF subarray (BMWSS) codebook in [12], and the beam pattern shaping approach (BPSA) codebook in [18] are selected
As the signal-to-noise ratio (SNR) increases, the beam alignment error probability (BAER) of BTOI decreases rapidly, which is much better than the traditional method
Summary
Millimeter wave (mmWave) communication is regarded as one of the most promising technologies for future wireless communication systems, and its abundant spectrum resources can significantly increase system capacity [1], [2]. One typical BT method uses an exhaustive search, where the transmitter sends all training beams in the codebook to cover the entire search range and selects the best beam [8]–[10]. Once the search interval is determined with error in a certain BT stage, each following stage will search in the wrong area This manifests as the error propagation problem in the traditional BT scheme, which limits the accuracy of beam alignment. It proposes to modify the main lobe of the beam to cover the transition band of the previous layer, which can help reduce error propagation This method results in a reduction of the beam gain, as well as the beam resolution. From the different training beams, the receiver can obtain an estimate of φ0 and feed the result back to the transmitter
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