NTT DoCoMo

About: NTT DoCoMo is a based out in . It is known for research contribution in the topics: Base station & Mobile station. The organization has 4032 authors who have published 8655 publications receiving 160533 citations.

On the Autoreducibility of Random Sequences

Abstract: A binary sequence $A=A(0)A(1)\ldots$ is called infinitely often (i.o.)~Turing-au\-to\-re\-duc\-ible if $A$~is reducible to itself via an oracle Turing machine that never queries its oracle at the current input, outputs either $A(x)$ or a don't-know symbol on any given input~$x$, and outputs $A(x)$ for infinitely many~$x$. If in addition the oracle Turing machine terminates on all inputs and oracles, $A$~is called i.o.~truth-table-autoreducible. We obtain the somewhat counterintuitive result that every Martin-L\"of random sequence, in fact even every rec-random or p-random sequence, is i.o.~truth-table-autoreducible. Furthermore, we investigate the question of how dense the set of guessed bits can be when i.o.~autoreducing a random sequence. We show that rec-random sequences are never i.o.~truth-table-autoreducible such that the set of guessed bits has positive constant density in the limit and that a similar assertion holds for Martin-L\"of random sequences and i.o.~Turing autoreducibility. On the other hand, we show that for any rational-valued computable function~$r$ that goes nonascendingly to zero, any rec-random sequence is i.o.~truth-table-autoreducible such that on any prefix of length~$m$ at least a fraction of~$r(m)$ of the $m$~bits in the prefix are guessed. We include a self-contained account of the hat problem, a puzzle that has received some attention outside of theoretical computer science. The hat problem asks for guessing bits of a finite sequence, thus illustrating the notion of i.o.~autoreducibility in a finite setting. The solution to the hat problem is then used as a module in the proofs of the positive results on i.o.~autoreducibility.

Service architectures in H.323 and SIP: A comparison

Abstract: One of the major challenges for next-generation IP networks is to provide new, attractive multimedia services. This includes traditional telephony (voice over IP) and the interworking with legacy telephony systems. In addition to the general problems regarding the support of realtime services in the IP network, e.g., quality of service, voice over IP focuses on the control of advanced features such as supplementary services well known from telephony and on the mechanisms for their fast and efficient development and deployment. The two most promising approaches in the area of multimedia over IP are the protocol suites H.323 (ITU-T) and SIP (IETF). Several comparisons of these two protocols have already been published, but comparisons of their service architectures have been rarely addressed. This tutorial describes and compares the service architectures of H.323 and SIP. The basic protocol architectures are explained, followed by an in depth evaluation of the service implementation mechanisms. The analyses focus mainly on the control of telephony supplementary services in H.323 and SIP and are backed up by detailed examples. Although the two protocol architectures are quite similar, it is shown that there are considerable differences regarding their supplementary service architectures. H.323 (together with H.450) has been especially focused on supplementary services, smooth interworking with the PSTN, and interoperability between different implementations. In this respect, it has clear advantages for IP telephony applications. SIP has been designed with a broader scope, providing more generic syntax and semantics regarding feature definition and session description. Since the SIP standards do not describe details of possible application and service features, this bears the danger of interoperability problems, e.g, for supplementary services. SIP offers advantages for non voice over IP services and applications. A coexistence of both protocols can be foreseen, stressing the importance of interworking between them.

Content distribution management device, terminal, program, and content distribution system

Abstract: A content distribution system according to the present invention comprises a content distribution management device and a communication terminal. The content distribution management device includes a storage unit that stores one or a plurality of addresses; a receiving unit that receives content data addressed to a communication terminal; a determination unit that determines whether or not the address of the origin of the received content data is an address that is stored in the storage unit; and a sending unit that, in the case where the determination unit has determined that the address of the origin of the received content data is an address that is stored in the storage unit, sends the content data and parameters specifying the format in which content is to be displayed by the communication terminal to which the content data is addressed to a communication terminal. The communication terminal includes a receiving unit that receives parameters and content data from the content distribution management device; and a content display control unit that displays the received content data and controls the display format thereof in accordance with the received parameters.

How backhaul networks influence the feasibility of coordinated multipoint in cellular networks [Accepted From Open Call]

Abstract: Interference is one of the most challenging problems in current cellular mobile access networks. Coordinated nultipoint transmission/ reception, and in particular joint processing, has proven to be a beneficial solution for interference management. Most research so far has investigated the requirements and gains on the wireless side but only superficially showed the impact on and requirements for the backhaul network. We take a different approach by looking at different backhaul topologies and technologies, and analyzing how they can support CoMP cooperation schemes. We study, for different traffic scenarios and backhaul connectivity levels, which base station clusters are actually feasible compared to the ones desirable from the radio access network perspective. We found out that a significant mismatch exists between the desired wireless clusters, as defined by the RAN, and feasible ones, as allowed by the given backhaul characteristics. Based on these findings, we explain how RAN clustering and backhaul clustering have to cooperate to come to feasible solutions. As one possible solution, we present a backhaul network preclustering scheme, which is able to predict which BSs are actually eligible for cooperation during the runtime of the network. The gains of this approach are quantifiable in terms of reduced signaling and user data exchange, and reduced MIMO signal processing.

Transmission apparatus and transmission method

Abstract: A transmitter transmits data to a communicating opponent with a better channel condition with use of one or more frequency blocks including one or more carrier frequencies. The transmitter includes a communicating opponent selection unit evaluating the channel condition for each frequency block for each of plural communicating opponents and selecting one or more communicating opponents from the plurality of communicating opponents, a modulation scheme determination unit determining at least a modulation scheme depending on the evaluated channel condition, a control channel generation unit generating a control channel indicative of the determined modulation scheme and one or more frequency blocks available for the selected communicating opponents to receive a data channel, and a channel transmission unit providing the selected communicating opponents with the control channel and the data channel modulated in accordance with the modulation scheme.