Performance Evaluation And Power Allocation In Distributed Antenna System Based On Channel Measurement

Distributed antenna system (DAS) has received widespread interest and attention for its capability to introduce diversity and enhance power coverage through decreasing access dis-tance. Especially for high frequency, DAS can overcome its drawbacks that it can be easily attenuated by distance or obstacles, to extend its coverage range. Based on channel measure-ment, performance of DAS at6GHz is researched in this paper, including:(1) Channel property analysis and modeling. In DAS, antennas are distributed geo-graphically and may have different propagation environment. Channel models for single link and multiple inputs and multiple outputs (MIMO) system cannot be applied to DAS directly to make it necessary to model for DAS individually. Based on measurement in indoor sce-nario, correlation of small scale fading and shadow fading between propagation links are in-vestigated. They both have a small correlation coefficient in the measured scenario, to make it possible to exploit macro-and micro-diversity gain. Besides, delay spread in DAS is investi-gated. Delay spread in DAS is small, compared with centralized antenna system (CAS) based on channel measurement. Finally, Rician K factor is analyzed in DAS. Since DAS can reduce access distance, it can make sure more LOS probability to combat flat fading.(2) Performance evaluation in DAS. Previous results in DAS are based on assumed channel models, which cannot provide precise performance evaluation. Therefore channel measurement is adopted in this paper. Compared with single antenna system (SAS), DAS has a good coverage ratio and uniformity. Especially in multi-floor scenario, its advantage is more obvious. Besides, with channel measurement conducted in the same floor, DAS have great advantage in capacity over single input multiple outputs (SIMO), and similar performance to MIMO.(3) Power allocation in DAS. Due to peculiar structure in DAS, a power allocation al-gorithm based on perfect large scale fading information is proposed firstly, for frequency se-lective fading channel. With measured data, the proposed algorithm has been verified. Com-pared with uniform power allocation scheme, the proposed algorithm can improve capacity greatly. Besides, a power allocation algorithm based on predicted large scale fading informa-tion through path loss models is introduced in DAS, which has similar performance to the scheme with perfect large scale fading information. Further more, effect of error in prediction on performance of the algorithm is examined.