Optical low-coherence ref lectometry is applied for the first time to our knowledge to investigate diffusive biological tissues with a single-mode fiber probe. Samples of fresh arteries are studied, using the backscattered light from the tissue. The probed volume in the vicinity of the fiber tip is estimated to be below 6.7 x 10(-10) cm(3). This noninvasive method allows one to determine optical parameters, such as the index of refraction and the transmission properties, and the tissue thickness.

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SUMMARYThis paper describes and evaluates a novel 2-dimensional radio resource allocation scheme for highthroughput cellular packet data access. The proposed system employs spread spectrum orthogonal frequency division multiplexing with adaptive time and frequency allocation (SS-OFDM-F/TA) of radio resources. In order to achieve high spectral efficiency of downlink packet transmissions to multiple mobile users, multi-user diversity available in the multi path fading environment is exploited through the use of adaptive modulation and coding, best serving sector selection, suitable scheduling of packet transmissions and hybrid ARQ employing soft-packet combining and incremental redundancy. The data throughput, packet delay and fairness of the system with slow and fast best sector selection are examined. A method of grouping disjoint sub-bands for use in highly frequency-selective environments is described and evaluated. Packet re-transmission options including a proposal of several asynchronous re-transmission algorithms and constraining the maximum re-transmission interval are also considered. It is demonstrated that the proposed spread spectrum OFDM system is capable of reaching a spectral efficiency of about 1.7 b/sec/Hz/ sector with single receive and transmit antennas, and seems to provide a promising solution for highthroughput best-effort delay-tolerant data services in future cellular radio systems.