Reuven Meidan

Frequency hopping CDMA for future cellular radio

A code-division multiple access (CDMA) system based on slow frequency hopping (FH) is proposed. The hopping sequences are selected such that all users of each cell are using mutually orthogonal codes, and intercell correlation of hopping sequences is minimal. FEC and interleaving are used to mitigate the remaining interference. It is shown that with proper selection of system parameters, FH-CDMA enjoys the advantages so far claimed by DS-CDMA, i.e. FH-CDMA capacity benefits from interference averaging and can take advantage of the duty cycle associated with voice activity. It also yields a sectorization capability and one-cell frequency reuse pattern. Moreover, due to the orthogonal operation, the interference from cell co-users is eliminated. Since this is the major source of interference in nonorthogonal systems like DS-CDMA, FH-CDMA yields higher capacity capabilities (35 times AMPS). Other advantages of FH-CDMA with its implementation as a cellular system are discussed.<<ETX>>

To spread or not to spread, this is the question

TDMA and DS-CDMA are two access methods proposed for digital cellular systems and given the status of standard in the U.S. It is shown in this paper that a capacity comparison between them is scenario specific. In the case of terrestrial cellular CDMA is the winner, whereas in the scenario of a single isolated cell, or for a satellite based cellular system, TDMA appears to be superior. Lastly, there can be a regulatory reason which can prevent the implementation of DS-CDMA like in the Private Land Mobile case, where spectrum is usually licensed on the basis of single narrowband channels and thus a contiguous wide band spectrum is not available.<<ETX>>

Comment on "Optimal Design of PLL with Two Seperate Phase Detectors"

This correspondence comments on a recent paper by Heiman and Bar-Ness. In the paper the authors propose a two-channel PLL and pursue an optimization analysis of the proposed configuration. They base the analysis on Viterbis equivalent noise model. In our comment it is shown that their application of the model suffers from a fundamental flaw. Difficulties in the physical interpretation of the results are demonstrated.