The WiDeS group is now investigating the feasibility of using this band for outdoor long-distance (>100m) links.
Link Budget Analysis
An example wireless link budget is shown below:
For this link budget analysis, 48 dB high-gain Cassegrain antennas are considered in the transmitter and receiver. As presented in this figure, millimeter-wave wireless data communication is possible up to approximately 300 meters.
We are furthermore working on experimental assessment of the transmission quality for different distances between source and destination.
For distances larger than 300m, the assistance of relays is required. We are working on relay selection schemes that exploit the fact that there is little interference between links (due to the highly directional antennas). Inter alia, we developed a polynomial-time algorithm that can select relays and their cooperation modes that maximize the total achievable video quality for multiple unicast flows in IEEE 802.11ad very high throughput (VHT) relaying systems (for more details, refer to the corresponding IEEE PIMRC-2011 paper), assuming that the number of relays is larger than the source-destination pairs.
We are currently working on generalizations of the algorithm to the case where there are fewer relays than source-destination pairs, and thus relays have to act as concentrators of video streams.
Polarized LOS (Line-of-sight) MIMO
MIMO system can provide an increase in spectral efficiency which, in principal, is proportional to the minimum number of antennas in transmitter and receiver sides. With a full scattering environment assumption in which channel matrix is full rank and each sub-channel is considered i.i.d. Rayleigh fading, this enhanced spectral efficiency can be achieved. However, in case of LOS (line-of-sight) channel, LOS components dominate fully scattering components and the effective channel rank may be reduced to one because of the linear dependencies among LOS sub-channels.
Driessen and Foschini showed in 1999 that, given properly allocated antennas at both ends, LOS channels allow spatial multiplexing and are particularly well-suited. A number of investigations have shown that high spectral efficiency and throughput can be achieved in LOS MIMO with relatively lower burden in pilot data transmission for synchronization due to low mobility.
Our research in this area spanned various range of topics and currently focuses on proposing algorithm and working receiver structure for achieving very high spectral efficiency and throughput. The proposed system adopts polarized LOS MIMO with very high-order modulation and each antenna is synchronized with different system clocks, which can allow multiple transmit and receive antenna sites are located geometrically far from each other. This system structure, however, causes a synchronization problem different from those in the conventional wireless system and demands a solution to this problem and highly accurate estimators because of polarization interference, high amplitude density, and asynchronous multiple transmission signals.
Our work in this area concentrates on an iterative joint maximum likelihood estimator (JMLE) combined with SIC(successive interference cancellation) for SFO (symbol frequency offset), CFO (carrier frequency offset) and CSI (channel state information) under different synchronization situations.