A multiple‐access modulation technique that uses multilevel frequency shift keying (FSK) to modulate frequency‐hopped, spread‐spectrum carriers is examined for possible application to digital mobile radiotelephony. This technique, in which all users employ the full system bandwidth simultaneously, would be resistant to the frequency‐selective fading so troublesome in mobile radio. We have studied base‐to‐mobile communication of 32 kb/s per user in the 20‐MHz (one‐way) bandwidth of the 850‐MHz mobile radio band. The number of users that can be served within a given bit error rate criterion depends on the quality of the radio channel. For perfect transmission, where the only degradation is mutual interference, an error rate less than 10−3 can be maintained with up to 209 simultaneous users. Transmission impairments, consisting of white Gaussian noise and frequency‐selective Rayleigh fading with an average rf signal‐to‐noise ratio of 25 dB, reduce the number of simultaneous users to about 170. This capacity is roughly three times that of a phase‐shift‐keying spread‐spectrum system recently proposed for mobile radio. For mobile‐to‐base transmission of FH‐FSK, we have yet to study impairments resulting from delay spread in a synchronous system or, alternatively, the penalty for operating asynchronously. These effects would reduce the number of possible users from the estimates we have given for base‐to‐mobile transmission.

The present study focuses on the evaluation of the effect of He-Ne laser on tissue regeneration by monitoring collagen synthesis in wound granulation tissues in Swiss albino mice using analysis of laser induced fluorescence (LIF) and light microscopy techniques. The spectral analyses of the wound granulation tissues have indicated a dose dependent increase in collagen levels during the post-wounding days. The histological examinations on the other hand have also shown a significant increase in collagen deposition along with the reduced edema, leukocytes, increased granulation tissue, and fibroblast number in the optimal laser dose treated group compared to the non-illuminated controls.

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An analytical technique based on Gram-Charlier series expansion is presented for the computation of the error probability of equal-gain combiner (EGC) with partially coherent fading signals. Imperfect carrier recovery is attributed to the random noise present in the carrier recovery loops. The resulting noisy phase references are assumed to satisfy Tikhonov distribution. The fades on the diversity branches are assumed to be slowly varying and statistically independent with Rayleigh-distributed envelopes. The error-rate performance of coherent and differentially coherent phase-shift keying (PSK) systems are compared and the phase precision requirement for a reliable coherent detection is computed. Detection loss caused by carrier phase errors is computed for several signal-to-noise ratio (SNR) reliability and bit error probability levels. It is demonstrated that the effect of carrier phase errors on the mean SNR is negligible compared to their effect on deep fades or small bit error probabilities. It is also shown that the carrier phase precision requirement can be reduced through signal combination.

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