Palavras-chave canal, MIMO, capacidade, número efetivo de multipercurso, espalhamento de retardos, espalhamento angular, perfil de potência de retardos, perfil de potência azimutal.
T set the basis for error performance standardization at the lower layers of B-ISDN networks. The specific performance parameters of these recommendations are directly related to the bit error rate and are strongly dependent on the level of correlation of the error sequence. Bit errors in typical satellite transmissions occur in bursts, and that should be taken into account when designing satellite ATM networks. Error modeling and analysis of G.826 and I.356 performance criteria and satellite design principles are reviewed.
Despite the continuous growth of data services, telephony is still the main source of revenue for the third generation mobile systems operators, particularly in the case of UMTS systems already deployed in the world [1]. Considering the increasing utilization of VoIP (Voice over IP), it is important to adequate the UMTS systems to this technology, in order to maximize the efficiency of transmission over the air interface. This paper considers a new contribution in this direction, based on the reduction of VoIP packet overhead, aiming to lower power consumption during a typical conversation. It is well known the advantages of HSPA systems for VoIP transmission, but at this moment there are only a few networks commercialy available using this technology.
The introduction of IMS (IP Multimedia Subsystem) in UMTS (Universal Mobile Telecommunication Services) architecture has made possible the implementation of end to end VoIP calls, thus integrating mobile and fixed networks in the IP technology. However we know that, without the use of some techniques, VoIP transmission can demand more resources, in terms of bandwidth and power. This is not a serious problem for fixed networks, but it is of special concern in the case of mobile systems, mainly because of the natural limitations of the air interface and the power restrictions of the user cellular equipment. In this paper we address the performance of voice calls in terms of transmitted power efficiency. We show that making convenient choices of standard procedures and using specific optimization techniques it is possible to turn IMS VoIP competitive with the traditional voice telephony service performed by the CS (Circuit Switching) counterpart of the UMTS.
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