Evaluation of adaptive techniques to improve the performance of indoor millimeterwave wireless communications systems

In this paper, the potential performance of indoor portable radio communications (IPRC) systems at millimeter wave frequencies with diversity and equalization techniques are investigated. A new transmission medium simulator is introduced based on millimeter wave propagation field measurements. The performances of coherent-BPSK (CBPSK), CQPSK, incoherent-MSK (IMSK) and Gaussian filtered IMSK (IGMSK) systems were studied by simulations and whenever possible,the results were compared with analyses. The CQPSK system was shown to perform better than CBPSK IMSK and IGMSK. However, in a typical office area with 50 ns delay spread, even CQPSK lacked sufficient capacity to support systems with connections to fixed networks such as ETHERNET (which communicates at 10 Mb/s). Hence, it was necessary to increase the transmission rate of the radio link to at least 10 Mb/s. We have shown that Gaussian pulse shaping did not increase the transmission rate of the MSK based systems in this delay spread environment. It was also shown that adaptive equalizers could not significantly improve the performance of IPRC systems significantly despite their sufficiently fast convergence rate. However, a significant improvement was realized when frequency diversity was employed. For millimetre wave systems operating in a one-cell-per-room scenario, signal attenuation through walls and ceilings exceeds 50 dB. Therefore, the entire available spectrum could be allocated to each cell, resulting in the maximum possible frequency diversity gain.