Philosophy

The paper investigates the performance of HIPER-LAN/2 (H/2) with sub-carrier based adaptive modulation, with respect to average throughput. The results obtained are compared with the case where the same modulation is used across all the sub-carriers as in the current H/2. We suggest a bit loading algorithm "Simple Rate Adaptive Algorithm" (SRA) based on the criteria of maximizing the throughput. Our work displays that this bit loading scheme improves the throughput compared to the existent H/2. The cost incurred is the complexity added by the adaptive modulation scheme. However, the total complexity of the system is decreased due to simplification in channel coding.

In this thesis we present the concept of concatenated multilevel codes. These codes are a combination of generalized concatenated codes with multilevel coding. The structure of these codes is simple and relies on the concatenation of two or more codes of shorter length. These codes can be designed to have large diversity which makes them attractive for use in fading channels. We also present an iterative decoding algorithm taylored to fit the properties of the proposed codes. The iterative decoding algorithm we present has a complexity comparable to the complexity of GMD decoding of the same codes. However, The gain obtained by using the iterative decoder as compared to GMD decdoing of these codes is quite high for Rayleigh fading channels at bit error rates of interest. Some bounds on the performance of these codes are given in this thesis. Some of the bounds are information theoretic bounds which can be used regardless of the code under study. Other bounds are on the error probability of concatenated multilevel codes. Finally we give examples on the implementation of these codes in adaptive coding of OFDM channels and MIMO channels.

Orthogonal Frequency Division Multiplexing (OFDM) allows transmission of data with high data rates over broadband radio channels without the need for powerful equalization. However, OFDM is sensitive to non-linearities in the system due to the high Peak to Average Power Ratio (PAPR) in the transmitted signal.

Iterative decoding of block codes is a rather old subject that regained much interest recently. The main idea behind iterative decoding is to break up the decoding problem into a sequence of stages, iterations, such that each stage utilizes the output from the previous stages to formulate its own result. In order for the iterative decoding algorithms to be practically feasible, the complexity in each stage, in terms of number of operations and hardware complexity, should be much less than that for the original non-iterative decoding problem. At the same time, the performance should approach the optimum, maximum likelihood decoding performance in terms of bit error rate.

This paper presents the construction and performance of rate adaptive generalized concatenated codes (GCCs) based on linear block codes over Rayleigh fading Multi Input Multi Output (MIMO) communication channels with N transmit and N receive antennas. The code design criteria is chosen such that it tries to follow the Shannon capacity of the MIMO channel. It is envisaged that such codes provide a superior performance over systems that use Maximum Ratio Combining (MRC) while maintaining the encoder/decoder complexity within an acceptable level of practical usage. Furthermore it is expected that these codes will provide good performance without an interleaver/deinterleaver because of their good burst error correction capabilities.

Can there be rules of language which serve both to determine meaning and to guide speakers in ordinary linguistic usage, i.e. in the production of speech acts? We argue that the answer is no. We take the guiding function of rules to be the function of serving as reasons for actions, and the question of guidance is then considered within the framework of practical reasoning. It turns out that those rules that can serve as reasons for linguistic utterances cannot be considered as normative or meaning determining. Acceptance of such a rule is simply equivalent to a belief about meaning, and does not even presuppose that meaning is determined by rules. Rules that can determine meaning, on the other hand, i.e. rules that can be regarded as constitutive of meaning, are not capable of guiding speakers in the ordinary performance of speech acts.

Some theories of linguistic meaning, such as those of Paul Grice and David Lewis, make appeal to higher order thoughts: thoughts about thoughts. Because of this, such theories run the risk of being empirically refuted by the existence of speakers who lack, completely or to a high degree, the capacity of thinking about thoughts. Research on autism during the past 15 years provides strong evidence for the existence of such speakers. Some persons with autism have linguistic abilities that qualify them as speakers, but manifest a severely impaired capacity to understand what it is to have beliefs.

Is the principle of semantic compositionality compatible with the principle of semantic holism? The question is of interest, since both principles have a lot that speaks for them, and since they do seem to be in conflict. The view that natural languages have compositional structure is almost unavoidable, since linguistic communication by means of new combinations of words would be virtually incomprehensible otherwise. And holism too seems generally plausible, since the meaning of an expression is directly connected with the way that expression interacts with other's to determine the meaning of more complex expressions. So, if these principles are in conflict, we have a problem.

This paper contains a discussion of how the concept of compositionality is to be extended from context invariant to context dependent meaning, and of how the compositionality of natural language might conflict with context dependence. Several new distinctions are needed, including a distinction between a weaker (e-) and a stronger (ec-) concept of compositionality for context dependent meaning. The relations between the various notions are investigated. A claim by Jerry Fodor that there is a general conflict between context dependence and compositionality is considered. There is in fact a possible conflict betwee ec-compositionality and context dependence, but not of the kind Fodor suggests. It turns on the presence of so-called unarticulated constituents, in John Perry's sense. Because of this phenomenon, on some semantic accounts there might be a variation in the meaning of a complex expression between contexts without any corresponding variation in any of the syntactic parts of that complex. The conflict can be resolved in several ways. One way is to make the unarticulated context dependence explicit only in the meta-language, which makes it into an unarticulated constituent account. A recent argument by Jason Stanley against such accounts is discussed. According to Stanley, certain readings of English sentences involving binding of contextual variables, are unavailable in these theories. After considering a reply to Stanley by François Recanati, I present an outline of a fully compositional theory, of the unarticulated constituent variety, which does deliver these readings. Concluding remarks on, inter alia, the semantics/pragmatics distinction.

Saul Kripke’s thesis that ordinary proper names are rigid designators is supported by widely shared intuitions about the occurrence of names in ordinary modal contexts. By those intuitions names are scopeless with respect to the modal expressions. That is, sentences in a pair like Aristotle might have been fond of dogs Concerning Aristotle, it is true that he might have been fond of dogs will have the same truth value. The same does not in general hold for definite descriptions. If we, like Kripke, account for this difference by means of the intensions of names and descriptions, we have to conclude that names do not in general have the same intension as any normal, identifying description. However, the difference in scope behavior between names and description can be accounted for alternatively by appeal to the semantics of the modal expressions. On the account we suggest, dubbed ‘relational modality’, simple singular terms, like proper names, contribute to modal contexts simply by their actual world reference, not by their (standard) intension. The relational modality account turns out to be fully equivalent with the rigidity account when it comes to truth of modal and non-modal sentences (with respect to the actual world), and hence supports the same basic intuitions. Given an alternative definition of consequence for relational modality, and a restriction to models with reflexive accessibility relations and non-empty world-bound domains, relational modality also turns out to be model theoretically equivalent with rigidity semantics with respect to logical consequence. Here we introduce the semantics, give the truth definition for relational modality models, and prove the equivalence results.

In this paper I shall be concerned with the relation between a particular account of linguistic meaning and the property of compositionality in natural language. 1 The account, proposed by Donald Davidson, is that based on considerations about radical interpretation. I shall argue that there is a fundamental conflict between, on the one hand, the view that the meaning of expressions of natural languages is determined purely according to canons of radical interpretation, and, on the other hand, the view that natural languages exhibit compositional structure. I shall also argue that if there is such a conflict, this speaks against the proposed account. 2

Are sensation ascriptions descriptive, even in the first person present tense? Do sensation terms refer to, denote, sensations, so that truth and falsity of sensation ascriptions depend on the properties of the denoted sensations? That is, do sensation terms have a denotational semantics? As I understand it, this is denied by Wittgenstein. Wittgenstein rejects the idea of a denotational semantics for public language sensation terms, such as‘pain’. He also rejects the idea that speakers can recognizesensations. I think these views are mistaken.In this paper I shall present the following: first, my own basic views on how public language sensation terms relate to sensations (section 1); second, to what extent these views are inconsistent with some of Wittgenstein's main tenets about sensations and sensation language, as set out in Philosophical Investigations##243–315, and what I take to be Wittgenstein's main arguments, in the same text, for those tenets (sections 2 and 3); third, why I think that those arguments are inconclusive (sections 4 and 5); and fourth, what I see as the best arguments for my own views (section 6). Sections 3 and 5 are concerned with the bearing of the private language argument on these matters.