CDMA Scheme Research Articles

Coherence coding for photonic code-division multiple access networks

We analyze a code-division multiple access technique where information is optically encoded by manipulating the coherence between a pair of transmitted signals. Key features are intrinsic security, operation of the receiver at only the bit rate of a single channel, and reconfiguration without switching optical delays, which are considerable advantages compared to previously proposed CDMA schemes. Experimental results demonstrating the basic operation of the scheme are presented. The performance limitations are calculated and novel implementations are proposed. >

Efficient Distributed Algorithms for Channel Assignment in Multihop Radio Networks

We present new distributed algorithms for the channel assignment or 'scheduling' problem in a radio network using TDMA. Both link and broadcast scheduling are addressed. As in [23], the algorithms are based on ordering the nodes of the corresponding graph on the basis of a criterion related to the 'reach' of the nodes. However, while [23] is inherently centralized, the algorithms given in this paper use a novel technique of partitioning into classes to yield efficient distributed implementations. Further, there is no compromise (in fact, for link scheduling there is an improvement) on the worst-case performance in comparison with the centralized algorithms of [23] which themselves represented a significant improvement over prior algorithms. In particular, the performance guarantee of our distributed algorithms is bounded by a constant times the graph thickness. Experimentally too, the performance is comparable to those of [23] and remains better than algorithms prior to it.A useful feature of our algorithms is that they are parameterized in a way that allows for the selection of a tradeoff between the schedule quality and efficiency. Also, the distributed algorithms are easy to implement and have low communication overhead. Finally, while only TDMA is discussed, it is highly possible that our 'class' based approach is applicable to CDMA and FDMA schemes as well.

Fiber-optic ladder networks for inverse decoding coherent CDMA

Coherent fiber-optic networks are used to improve upon incoherent CDMA schemes. If a single-channel network is used between transmitters and receivers, standard coherent correlation takes place. If several parallel spatial channels (fibers and/or polarizations) are used, ideal inverse decoding can be implemented, with perfect delta -function response of the matched decoder. The two-channel case is studied in detail. The rules for finding inverses of a given coding network and the relationship between matched networks for one-channel decoding and two-channel inverse decoding are given. Phase and frequency differences among stations imply that unwanted signals add up incoherently. The ideal two-channel network with inverse decoding has no loss due to encoding/decoding, only inevitable loss due to the broadcast network. In experiments using a single fiber between a transmitter and a receiver by orthogonal polarizations, delta -function inverse response was observed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>