Jürg Meierhofer

Link quality control for wireless ATM networks

The data link control (DLC) scheme is essentially needed in the protocol stack of wireless ATM systems in order to overcome the incompatibility between the ATM design assumptions and the characteristics of the physical radio channel. In this paper, the DLC scheme developed for the ACTS project Magic WAND (wireless ATM network demonstrator) is evaluated by taking into account a finite state radio channel model which allows to describe the radio transmission quality by a stochastic process. Due to the fact that the transmission quality for two subsequent time slots becomes correlated, this channel model is especially suited to evaluate the performance of error control and retransmission schemes. In particular, we compared the transmission scheme without error control to a scheme with a limited ARQ (automatic repeat request) mechanism by evaluating the cell loss ratio. When considering network services with different maximum delay requirements, these results allow to determine for which services ARQ schemes are beneficial.

Medium access control for wireless extensions of ATM networks

Wireless access to broadband communication networks is becoming an important issue. This paper discusses medium access aspects for a wireless extension of high-speed asynchronous transfer mode (ATM) networks. A centralized control scheme for a coordinated medium access is required in order to efficiently accommodate ATM traffic on wireless links. It turns out that the scheduler algorithm needed for the coordinated access strongly influences the cell delay which is most important for delay sensitive services. The performance of a first-come first-serve scheduler in terms of cell delay is analyzed for video-phone services. By modelling the cell stream of each terminal with an independent Bernoulli process the average queue length and cell delay can be evaluated in terms of the burstiness of the sources.

From Data Science to Value Creation

Value creation with data science methodologies generates important insights. However, these insights do not systematically provide service value to customers. Therefore, we show a systematic approach to use data science for the process of service design. We develop a structure of data science methodologies in the dimensions of their potential to create service benefit. This enables the mapping of the value contribution of the data science tools on the different perspectives and phases of the service design process. Based on this mapping, a direct link can be established between the outcomes of the data science methodologies and the value drivers for the customer. The resulting new methodology allows the systematic value creation from insights generated by data science.

Priority scheduling algorithm for ATM wireless network access

This paper discusses medium access issues for wireless asynchronous transfer mode (ATM) networks. In particular, a priority scheduling algorithm for a centralized access scheme has been analyzed using the Markov chain theory and the OPNET simulation package. The scheduler allocates resources to the terminals according to their priority class. Different algorithms (first-come first-serve, round robin, select largest queue) are proposed for scheduling the ATM traffic within the same priority class. The performance measures are cell delay, queue length, and cell loss ratio (CLR). It turns out that the scheduler algorithm strongly influences the cell delay which is most important for delay sensitive services. The CLR due to buffer overflows can be kept very low in general except for very bursty sources.

HYPERFLOW: An Efficient Error Control Protocol for Wireless Broadband Access Networks

The subject of this paper is the design and evaluation of an efficient errorcontrol scheme for indoor cellular wireless broadband access networks, whichcan be considered as the wireless extension of a fixed quality-of-serviceoriented network (e.g., based on the ATM- (asynchronous transfer mode-)protocol). In order to improve the high and time-variant probability of transmissionerrors, a novel error control scheme is developed. The protocol calledHYPERFLOW (Hybrid Partial sElective Repeat ARQ with Flow control) representsan efficient combination of a selective repeat and a Go-Back-N ARQ- (automaticrepeat request-) scheme while keeping the implementation complexity withinlimits. Additionally, it features a flow control mechanism which prevents the channel from being blocked by a user with momentarily hightransmission error probability and thus considerably increases the totalsystem throughput. Furthermore, the HYPERFLOW-protocol is combined with anadaptive forward error control code. The resulting type II hybrid ARQ-schemeis based on the principle of incremental redundancy with redundant symbolsbeing sent only when they are required.A realistic model for the fluctuations of the transmission quality is used forthe performance evaluation of the HYPERFLOW-protocol. It turns out that the adaptive FEC-based error correction scheme can considerably improve thesystem performance.The mean transmission delay, for instance, can be reduced by a factor of upto 10 when the FEC-scheme is properly applied.

End-to-End Methodological Approach for the Data-Driven Design of Customer-Centered Digital Services

The collection, analysis, and interpretation of digital data has become an important factor for the provision of services. However, there is a lack of methodologies for using data analytics systematically in an end-to-end process for designing services. Therefore, in this paper, we develop a conceptual approach covering the innovation funnel from idea generation to market deployment. In particular, we describe how qualitative approaches alternate with quantitative approaches along the innovation process. We pay special attention to the design of data-driven value propositions including the analysis and modeling of the customer needs, a phase in which the concept of hidden needs and pains is applied. To conclude, we propose the development of a tool to support and industrialize the approach discussed in this paper.

Fluid flow model and queueing analysis of an error control scheme for wireless broadband access networks

The subject of this paper is the development of a traffic model for indoor wireless broadband access networks, which can be considered as the wireless extension of a fixed quality-of-service oriented network (e.g., based on the ATM asynchronous transfer mode protocol). Mobile users communicate with corresponding users in the fixed network via an access point. A central scheduler in the base station is responsible for the fair assignment of transmission capacity to the users according to a dynamic time division multiple access scheme. In order to improve the high and time-variant probability of transmission errors, an error control scheme based on an efficient combination of a go-back-N and a selective repeat ARQ (automatic repeat request) scheme is applied. Additionally, the protocol features a flow control mechanism which dynamically adapts the transmission rate of a connection to the link quality. This prevents the channel from being blocked by a user with momentarily high transmission error probability, and thus considerably increases the total system throughput. The traffic model developed in this paper is based on the fluid flow approximation and provides a stochastic process describing the arrival stream of a connection taking into account both the bursty characteristics of the traffic sources and the retransmission traffic. The retransmission traffic is modelled by a realistic radio channel, taking into account the time-variant fluctuations resulting from the movements of the user. The traffic model allows one to calculate the total system load, including the re-transmission traffic. It turns out that there is good agreement between the calculated values and those obtained by simulation. Furthermore, the traffic model is used for a queueing model of the wireless broadband access network based on the diffusion approximation. The queueing analysis provides a good approximation of the distribution of the buffer length observed in the real system. Copyright