General Capacity Formula Research Articles

Reverse-link capacity of multiband overlaid DS-CDMA systems

In the future deployment of wideband DS-CDMA mobile communication systems, spectrum overlay among sub-bands with different bandwidths is probably inevitable. In this paper we present an approach to estimate the reverse-link capacity of overlaid multiband DS-CDMA systems in terms of the maximum number of users in each sub-band. We will derive the general capacity formula, and present a decomposition method for the capacity analysis to reduce the computational complexity. Based on this decomposition method the conditions for maximum bandwidth utilization are obtained. These results are then extended to account for realistic constraints such as the maximum received power and imperfect power control.

On the capacity of some channels with channel state information

We study the capacity of some channels whose conditional output probability distribution depends on a state process independent of the channel input and where channel state information (CSI) signals are available both at the transmitter (CSIT) and at the receiver (CSIR). When the channel state and the CSI signals are jointly independent and identically distributed (i.i.d.), the channel reduces to a case studied by Shannon (1958). In this case, we show that when the CSIT is a deterministic function of the CSIR, optimal coding is particularly simple. When the state process has memory, we provide a general capacity formula and we give some more restrictive conditions under which the capacity has still a simple single-letter characterization, allowing simple optimal coding. Finally, we turn to the additive white Gaussian noise (AWGN) channel with fading and we provide a generalization of some results about capacity with CSI for this channel. In particular, we show that variable-rate coding (or multiplexing of several codebooks) is not needed to achieve capacity and, even when the CSIT is not perfect, the capacity achieving power allocation is of the waferfilling type.

A further generalization of Tanner’s formula

A general capacity formula for the case of more than one major lane is derived, using the M3 distribution and allowing the major lanes to differ in critical gaps and follow-up times. The derivation can be further extended to there being different minimum headways for the major lanes and to distributions other than the M3 distribution. It is shown that the resulting formulas provide more accurate capacity estimations.

Queueing at unsignalized intersections

A general queueing theory model for traffic flow at unsignalized intersections is described and analysed which contains most of the mathematical models developed in the literature as special cases. Thus a consistent approach is presented for obtaining these models from a general viewpoint. Included are green-red models which are based on an analogy to traffic signals. Critical gaps and merging times or move-up times are allowed to be stochastically dependent. Inconsistent and consistent driver behaviour is considered. Platooning of the major road traffic with random intra-bunch headways is included. The results focus on the distributions of queue lengths and delays and, in particular, on capacities. A general capacity formula is developed and it is shown how the various capacity formulas from the literature come out as special cases. Some numerical results are presented.