In this paper are introduced fundamentals, characteristics, advantages and disadvantages of Multiple Access (MA) employed as transmission techniques in the Maritime Mobile Satellite Communications (MMSC) between ships and Coast Earth Station (CES) via Geostationary Earth Orbit (GEO) or Not-GEO satellite constellations. In fixed satellite communication, as a rule, especially in MMSC many users are active at the same time. The problem of simultaneous communications between many single or multipoint mobile satellite users can be solved by using MA technique, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Space Division Multiple Access (SDMA) and Random (Packet) Division Multiple Access (RDMA). Since the resources of the systems such as the transmitting power and the bandwidth are limited, it is advisable to use the channels with complete charge and to create a different MA to the channel. This generates a problem of summation and separation of signals in the transmission and reception parts, respectively. Deciding this problem consists in the development of orthogonal channels of transmission in order to divide signals from various users unambiguously on the reception part.
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Wireless ad hoc networks are frequently deployed in strategic applications that require the use of battery powered nodes. A key requirement for these networks is to maximize the time span when all nodes have sufficient battery charge to participate in communication with other nodes. To meet this requirement, this paper describes a routing strategy that seeks to find the best balance between minimizing the power consumption and evenly using all nodes within the network to avoid early exhaustion of individual nodes. The proposed routing scheme is compared to reported schemes using minimum power routing and the results show that the proposed scheme gives a longer time until the first node’s battery energy is depleted with a lower network power consumption than schemes using just energy minimization. Multiple access techniques are discussed and a cost-effective scheme based on available wireless LAN channels and space division multiplexing is proposed. Each path can use one, two or three time slots according to the number of hops in the path. Adaptive modulation is used where the link power budget is sufficient to maintain the throughput per unit time regardless of the number of hops in the path. Simulation results show that the throughput can be significantly improved using adaptive modulation with a small reduction in the time until the first node’s battery energy is depleted.
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