Ballot theorems applied to the transient analysis of nD/D/1 queues

The problem of transporting constant-bit-rate (CBR) traffic through a packet network is analyzed. In the system considered, CBR traffic is packetized and packets from several similar sources are multiplexed on a transmission link. The bit streams are recreated at the receiving end by demultiplexing the packets and then playing out the packets of each CBR stream. Traffic fluctuations may cause gaps to appear in the playout process. Their frequency can be reduced by adding a smoothing delay to each stream. The queueing system analyzed has periodic arrivals and deterministic service times. A method of analysis, based on the ballot theorems of Takacs (1967), is presented to provide steady-state delay distributions as well as a transient analysis of the system to predict the statistics of the time for a gap to develop in the CBR stream as a function of the smoothing delay     

On the Robustness of Scheduling Against Channel Variations

In this paper, we study the robustness of scheduling against channel variations. Specifically, we consider a class of generalized proportional fairness (PF) schedulers that achieve optimal throughput-fairness trade-off and study their robustness in terms of maintaining a certain fairness criterion when the channel statistics change from the additive white Gaussian noise (AWGN) to Rayleigh fading for all users. We conclude that the scheduler is robust only when it is configured to achieve the proportional fairness. For the other scheduler configurations, which are not robust, we show how fairness deviates from the ideal one when the channel statistics change and show how scheduler parameters need to be adjusted to restore the desired fairness. We also show simulation results.     

Amplifier induced crosstalk in multichannel optical networks

The effect of crosstalk introduced due to gain saturation in an optical amplifier when it is used for amplifying multiple channels in a wavelength division multiplexed (WDM) network employing ON-OFF keying with direct detection is studied. The system power penalty is quantified as a function of the amplifier input power, the number of channels, and the extinction ratio     

V.92: the last dial-up modem?

Ever since the first dial-up modems appeared in the 1960s, their obsolescence has been repeatedly predicted. However, contrary to such predictions, dial-up modems thrived in the 1980s and 1990s as a result of the slow rollout of residential digital services and the unprecedented growth of internet and remote access. Since the first 300 b/s dial-up modem standard (V.21), modem speeds have increased steadily. Most recently, International Telecommunications Union (ITU) Recommendation V.90 (1998) takes advantage of the direct digital-network connection of an internet service provider (ISP) remote-access server to achieve speeds of more than 50 kb/s downstream (from ISP to a user). However, for upstream transmission (from a user to ISP), V.90 employs the older V.34 modulation (1994), which typically delivers on the order of 30 kb/s. A new ITU modem standard called V.92 increases upstream rates to above 40 kb/s, again by taking advantage of pulse code modulation connections. In this paper, we present the transmission scheme that has been adopted for V.92. It involves a generalization of Tomlinson-Harashima precoding. We predict that V.92 will be the last dial-up modem standard. However, we have to wonder whether we might be falling into the same trap into which many others have fallen in the past. The future will be the judge!.     

Initial synchronization of DS-CDMA via bursty pilot signals

We consider initial timing acquisition in discrete-sequence code-division multiple-access (DS-CDMA) when propagation is affected by multipath and fading, and where the base-station broadcasts a synchronization pilot signal in the form of bursts of modulated chips transmitted periodically and separated by long silent intervals. Subject to certain simplifying assumptions, we derive the maximum-likelihood (ML) estimator by solving a constrained maximization problem. Our ML timing estimator has constant complexity per observation sample. The relation to other estimation methods is addressed, and performance comparisons are provided by simulation. The proposed estimator yields good performance independently of the multipath-intensity profile of the channel, provided that the delay spread is not larger than a given maximum spread. Moreover, our estimator is fairly robust to the mismatch in the fading Doppler spectrum and provides good performance for both fast and slow fading     

Routing subject to quality of service constraints in integratedcommunication networks

With increasingly diverse QOS requirements, it is impractical to continue to rely on conventional routing paradigms that emphasize the search for an optimal path based on a predetermined metric, or a particular function of multiple metrics. Modern routing strategies must not only be adaptive to network changes but also offer considerable economy of scope. We consider the problem of routing in networks subject to QOS constraints. After providing an overview of prior routing work, we define various QOS constraints. We present a call architecture that may be used for QOS matching and a connection management mechanism for network resource allocation. We discuss fallback routing, and review some existing routing frameworks. We also present a new rule-based, call-by-call source routing strategy for integrated communication networks     

An open software-radio architecture supporting advanced 3G+ systems

This paper describes a software-radio architecture developed for providing real-time wide-band radio communication capabilities in a form attractive for advanced 3G systems research. It is currently being used to implement signaling methods and protocols similar, but not limited to, evolving 3G radio standards (e.g. umts, cdma2000). An overview of the hardware system is provided along with example software implementations on both high-perfo-mance DSP systems and conventional microprocessors.     

Models of blocking probability in all-optical networks with andwithout wavelength changers

We introduce a traffic model for circuit-switched all optical networks which we then use to calculate the blocking probability along a path for networks with and without wavelength changers. We investigate the effects of path length, switch size, and interference length (the expected number of hops shared by two sessions which share at least one hop) on blocking probability and the ability of wavelength changers to improve performance. Our model correctly predicts unobvious qualitative behaviour demonstrated in simulations by other authors