A tight upper bound on the decoding error probability is derived for block-coded modulation structures where an M-ary phase shift keying (M-PSK) signal constellation is employed. This bound, called a tangential sphere bound, is tight for very low (as well as for high) signal-to-noise ratios (SNRs). Berlekamp's tangential union bound, previously derived for binary codes, can be derived for an M-PSK block coded modulation structure as well. However, it is proven that our tangential sphere bound is tighter than Berlekamp's (1980) tangential bound. For particular schemes, it is shown that for low SNRs our bound is considerably tighter than the tangential bound. As one of the examples, a multistage decoder is considered.

Transmission of information through a multiple-access-modulo-2 adder channel is addressed for the situation that out of a fixed family of N potential users at most some m, m>

Two techniques for upper bounding the average probability of decoding error in coded modulation structures are presented. The first bound, which is applicable to the additive white Gaussian noise (AWGN) channel, is tighter than the well-known union bound and the minimum distance bound, especially for low signal to noise ratio. It is shown that for the Leech lattice this upper bound is very close to a sphere lower bound. For the second upper bound, which is applicable to any memoryless channel (not necessarily AWGN), a method of random coset coding is presented. For the AWGN channel, a tighter upper bound is obtained by employing the method of random coset coding for calculating the average spectrum of distances of the code, which is required for the computation of the first upper bound.>

Many coded modulation constructions, such as lattice codes, are visualized as restricted subsets of an infinite constellation (IC) of points in the n-dimensional Euclidean space. The author regards an IC as a code without restrictions employed for the AWGN channel. For an IC the concept of coding rate is meaningless and the author uses, instead of coding rate, the normalized logarithmic density (NLD). The maximum value C/sub /spl infin// such that, for any NLD less than C/sub /spl infin//, it is possible to construct an PC with arbitrarily small decoding error probability, is called the generalized capacity of the AWGN channel without restrictions. The author derives exponential upper and lower bounds for the decoding error probability of an IC, expressed in terms of the NLD. The upper bound is obtained by means of a random coding method and it is very similar to the usual random coding bound for the AWGN channel. The exponents of these upper and lower bounds coincide for high values of the NLD, thereby enabling derivation of the generalized capacity of the AWGN channel without restrictions. It is also shown that the exponent of the random coding bound can be attained by linear ICs (lattices), implying that lattices play the same role with respect to the AWGN channel as linear-codes do with respect to a discrete symmetric channel.>

Bounds on the error probability of maximum likelihood decoding of a binary linear code are considered. The bounds derived use the weight spectrum of the code and they are tighter than the conventional union bound in the case of large noise in the channel. The bounds derived are applied to a code with an average spectrum, and the result is compared to the random coding exponent. The author shows that the bound considered for the binary symmetrical channel case coincides asymptotically with the random coding bound. For the case of AWGN channel the author shows that Berlekamp's (1980) tangential bound can be improved, but even this improved bound does not coincide with the random coding bound, although it can be very close to it.>

The coding problem for the binary degraded memory (DM) or write-once-memory (WOM) under a partial modification of records is considered. For this memory, if '1' is recorded in any cell then the content of this cell cannot be changed during following recordings. Double recording into such a memory with specified constraints is considered. Upper and lower bounds for the capacity of the DM under this kind of recording are derived. The lower bound is derived only for the case where the size of input messages alphabet is going to infinity.>